This invention relates to a carpenter's square and protractor which can accurately duplicate an angle onto a surface. More particularly, it relates to a combined square and protractor for use with the layout and cutting of large panelling in which the T-head of the square is secured with respect to the center of the ruler so that an accurate angular relationship is at all times maintained between the T-head surface edge and the intersecting ruler edge, as well as providing a supporting wall surface so that projections can extend therefrom thereby providing a means of locating the center of a large circle, such as a table.
Carpenter's squares which are currently available and which also provide a protractor function usually employ a center slotted ruler with a protractor element rotatively mounted thereon and with a draw bolt adjustment to the side of the ruler with a lug-like element positioned in the slot. Tightening of the draw bolt maintains the flat straight edge surface of the protractor element in any desired angular relationship to the ruler surface. A problem arises with the lateral or transverse attachment of the protractor element to the ruler in that when an accurate angular relationship is required, a tightening of the adjustment bolt from one side can cause an undesired movement between the straight edge of the protractor and the straight edge of the ruler thereby preventing accurate duplication of the desired angle onto the work surface. The foregoing problem becomes even more magnified when large surfaces are worked upon or cut such as with panel board. It is obvious that a minor discrepancy between the T-head and the ruler portion of the square when projected over several feet can result in a major error and problem in marking and cutting the board at the desired angle. Further, many carpenter's protractor squares involve the use of dual adjustment and tightening screws thus adding to the cost of the unit.
It is an advantage of the present invention to provide an improved combination carpenter square and protractor. It is an additional advantage of this invention to provide a device of the aforementioned type wherein the protractor portion of the square is secured to the ruler portion in a manner such that a distortion of the protractor straight edge surface with respect to the ruler edge surface is avoided upon tightening the two elements together. Other advantages are a tool of the aforementioned type which will also provide a unique slide arrangement between the protractor element and the ruler; a means of providing a center locating device for circular surfaces such as round tables; an improved combination panel square and protractor which affords both level vials and plumb vials in the T-head cross member and also affords attachment of an additional protractor dial for determining angular relationships separate from the square and protractor.